For example, very low testosterone levels or testosterone deficiency is associated with low energy, reduced libido, poor concentration, and fatigue.

Testosterone is also critical to building muscle mass and strength and bone density. Testosterone levels naturally decline in men aged 40 and over by about 1% to 2% per year.

Sleep Affects Testosterone Levels

In the study, published in the Journal of the American Medical Association, researchers compared testosterone levels in a group of 10 healthy young men after a week of normal sleep and a week of sleep loss.

In the first week, the participants slept eight hours each night at home. Then they had three nights of 10-hour sleep and eight nights of 5-hour sleep in a sleep laboratory.

The results showed that testosterone levels decreased by 10%-15% after the week of sleep loss compared with their rested states. This decrease in testosterone levels was also associated with a loss of vigor among the participants.

Researchers say about 15% of adult workers in the U.S. get five hours or less of sleep per night, and this study suggests this kind of prolonged sleep loss could have a negative consequence on testosterone and men's well-being.